Selective signal tuning device

ABSTRACT

A receiver control apparatus is disclosed for locating an emitted signal by utilizing an automatic tuning means with a mechanical clutch mechanism will release the receiver tuning means after the frequency has been found.

Unite ttes tent Foley Oct. 24, 1972 [22] Filed:

[54] SELECTIVE SIGNAL TUNING DEVICE [72] Inventor: Nelson D. Foley, North Little Rock,

Ark.

[73] Assignee: The United States of America as represented by the Secretary of the Navy Nov. 2, 1954 [21] Appl. No.: 466,460

[52] US. Cl ..325/470, 325/344 [51] Int. Cl. ..H04b 1/32 [58] Field of Search ..250/20.41 A, 20.36, 20.52;

[56] References Cited UNITED STATES PATENTS 2,207,467 7/ 1940 Muller ..250/20.52 X

MAGNETIC 5 CLUTCH BAND REJECTION FILTER' 150K:

DIFFERENCE NETWORK Primary Examiner-Carl D. Quarforth Assistant Examiner-J. M. Potenza Att0rneyQ. B. Warner and Q. E. Hodges [5 7] ABSTRACT A receiver control apparatus is disclosed for locating an emitted signal by utilizing an automatic tuning means with a mechanical clutch mechanism will release the receiver tuning means after the frequency has been found.

2 Claims, No Drawings I l l 3 l BAND PASS FlLTER I 6 l i I soKc 5 w v l.

B y NOISE f SIGNAL AMPLlFlER AMPLIFIER Z ONE SHOT MULTIVIBRATOR PATENTEDnm 24 m2 SHEET 1 OF 2 NOISE AMPLIFIER BAND REJEOTION FILTER DIFFERENCE NETWORK ONE SHOT MULTIVIBRATOR FIG. I.

' BAND PASS FILTER l I soxc i SIGNAL AMPLIFIER NELSON D. FOLEY EXTOR By Q S WW ATTORNEYS PATENIEDncI 24 m2 SHEET 2 [IF 2 1 NVENTOR NELSOND. FOLEY Km (Q 7% w (1AM ATTORNEYS SELECTIVE SIGNAL TUNWG DEVICE The present invention relates generally to automatic tuning means for radio receivers, and more particularly to an improved signal actuated receiver control apparatus.

In connection with the firing of sondes or proximity fuzes from ordnance projectiles it is often desirable to obtain data indicative of the behavior of said sondes or fuzes in flight. Often a wealth of information can be derived from a radio signal emitted from such sondes or fuzes and received at a remote point, usually a ground station. While at first sight it would not appear difficult to tune a receiver to a preset sonde or fuze transmission frequency, this course is not practicable for the reason that while theoretically a sonde or fuze may be designed to emit a signal at a known frequency, generally, in operation, radiated frequency differs from the design frequency due to variations in impedances of certain of the components, as for example, the battery.

As will be obvious, great haste is necessary in adjusting the receiver to the frequency of the radiated signal. Thus, in the past, attempts to tune the receiver to a sonde or fuze signal have resulted in the lost of data concerning the early history of the projectile flight, because of the time lag occasioned in correctly tuning the receiver.

One of the principal objects of the present invention, therefore, is to provide a receiver control apparatus embodying a quick-acting automatic tuning means, actuated mechanically through a clutch, which will function to release the receiver tuning control immediately after the frequency of the emitted signal has been found.

Another object of the invention resides in the provision of a receiver control apparatus which will respond to a signalhaving a subcarrier modulation, but which will be unaffected by other common types of modulation.

A further object is to provide automatic tuning means which will be simple in arrangement and positive in operation.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of the present invention; and

FIG. 2 is a circuit schematic, only that portion of the receiver which is necessary to having understanding of the invention being shown.

In FIG. 1, portions of a convention FM receiver are illustrated together with blocks representing in functional form the present invention. The receiver, shown generally at 1, includes a conventional variable capacitor 2 for tuning the receiver and an output cathode follower 3. The signal output of the receiver 1 is constituted by a 50 KC subcarrier signal when tuned to the sonde frequency or by a random noise signal characterized in part by a spectrum extending from direct current to 300 KC when detuned. The receiver output is applied simultaneously to a band rejection filter 4, and, after passage through a blocking capacitor 5 to remove direct currents from said signal, to a band pass filter 6. The filter 6 is tuned to pass frequencies near the 50 KC subcarrier frequency. The filter 4 is tuned to pass all signals extending from zero to 300 KC, with the exception of those frequencies near 50 KC. The amplifier receiving the output of the filter 6 is designated as the signal amplifier 7. Similarly, the amplifier receiving the output of the filter 4 is designated the noise amplifier 8. The outputs of the amplifiers 7 and 8 are unidirectional voltages of positive polarity. The difference between the output of amplifier 7 and the output of amplifier 8 is obtained by means of a suitable network 9. A oneshot multivibrator 10 receives the output of 'the network 9 and is rendered operative, or conductive, by the appearance at the input thereof of a negative voltage. Whenever the multivibrator 10 is in a conductive state, current flow is established through the magnetic clutch 11, rendering the clutch rigid and hence capable of transmitting torque from the tuning control 12- to the shaft 13 of tuning condenser 2. That is, the magnetic clutch contains fine particles of iron suspended in a suitable liquid such as oil, the whole being surrounded by-a magnetizing coil. When current flows through this coil, the magnetic particles form a rigid mass which causes the driving element of the clutch to carry along the driven element. However, when the magnetism is destroyed by stoppage of the current, the mass again becomes semi-liquid and no longer can serve as a mechanical connection between the clutch members.

Briefly, the operation of the tuning apparatus of the present invention involves a coarse tuning adjustment of the receiver to the frequency expected to be radiated from the sonde. Whenever the receiver is tuned off channel, the output thereof will be characterized by the appearance of noise. In this'condition, the output of amplifier 8 exceeds the output of amplifier 7 thereby resulting in the application of negative voltage to the multivibrator l0, rendering the clutch rigid and the receiver tunable. However, if the receiver is tuned to a channel occupied by a signal having an output characterized by a 50 KC modulation, the output of amplifier 7 exceeds the output of amplifier 8 and results inthe application of positive voltage to the multivibrator l0, cutting off any current flowing through the clutch magnetizing coil, and hence disengaging control 12 from shaft 13. Therefore, if the receiver is initially tuned off channel, and is subsequently tuned on channel, the tuning control 12 automatically will disengage from the shaft 13. The loss of signals resulting from tuning the receiver through the channel and beyond is thereby prevented.

In FIG. 2 there appears a more detailed presentation of the apparatus described with reference to FIG. 1. The signal amplifier is shown in the upper portion of the circuit, the noise amplifier being shown below it. The power supply is shown at the right. The receiver output is coupled to the filter 6 through blocking capacitor 5 and to filter 4 through resistor 19. Capacitor 5 prevents the application of any direct currents to the signal amplifier through the filter 6, while both alternating and direct voltages are applied to the filter 4. The filter 6 comprises a conventional band pass filter constituted by inductors 20, 21, 22, 23, and 24, and capacitors 25, 26, 27, 28, and 30.

The output of filter 6 produces a voltage drop across a potentiometer 29 which provides a convenient means of adjusting the voltage applied to the grid of V The output of V is fed from its anode 31 to the grid 32 of V through a coupling network 9 comprising a capacitor 33 and a resistor 9. The resistor 9 is shunted by a diode V having its cathode 34 connected at the junction of capacitor 33 and resistor 9', the anode 35 of said diode being connected to the opposite end of said resistor. Therefore, while the resistor 9' is chosen to present a considerable impedance to the flow of positive current therethrough, the flow of negative current is effectively short circuited by the parallel diode V The result is that only positive currents conducted through the capacitor 33 are effective in controlling the succeeding tube V The band rejection filter 4 comprises, conventionally, a chain of inductors 36, 37, 38, and 39, suitably shunted and by-passed by capacitors 41, 42, 43, and 44. The noise amplifier including its rectifying means is constituted by tubes V V V and V By virtue of the common cathode connection 45 of tubes V and V the output appearing at the anode 46 of V constitutes, in part, the difference between the voltages ap plied to the grids of V and V The rectifying means comprises a resistor 47 connected to the output of the filter 4 and to the anode 48 of diode V the cathode 49 of which is returned to a low impedance source of bias voltage 51.

Since at the center frequency the discriminator output of the FM receiver 1 is biased about 150 volts above ground potential, due to the cathode follower 3 it is necessary to return the junction of the diodes V and V to a low impedance point of equal DC voltage. The required voltage can be conveniently obtained from a voltage divider 51 in the regulated power supply. The power supply need not be described further, as it may be of conventional nature, using a full, wave rectifier V and two voltage regulating tubes V and V The diode V and resistor 47 constitute a voltage divider so that whenever a positive voltage appears at the output of filter 4 the diode V readily conducts and thereby presents a very low impedance with the result that very little voltage is applied to the grid of V On the other hand, whenever a negative voltage appears at the output of filter 4, the diode V is nonconductive and hence presents a high impedance thereby resulting in the application of a relatively great voltage to the grid of V Similarly, resistor 52 is connected to the output of the filter 4 with its opposite end returned to the bias voltage source through diode V The connection of V however, is opposite that of V That is, the cathode 53 is connected to the bias voltage source. Therefore, the operation of the voltage divider comprising resistor 52 and diode V will be opposite that of the above described voltage divider. Namely, that the appearance of positive voltages in the output of filter 4 results in the application of a voltage to the grid of v whereas negative voltages are effectively short circuited.

The noise amplifier constituted by triodes V and V produces at the anode 46 of triode V a voltage which is proportional to the difference between the voltages applied to the grids of said triodes. Therefore, since a positive voltage is applied to one grid (V and a negative voltage is applied to the other grid (V the output appearing at anode 46 is equivalent to the output of a full wave rectifier which has been amplified many times. An adjustable resistor 54 and a capacitor 55 are connected from'the anode 46 to ground to provide an adjustable filter for smoothing the output of V The output of the noise amplifier, V and V is coupled to a cathode follower V through a biasing arrangement comprising a battery 56. The bias applied to V is sufficient to maintain V nonconductive until a substantial output appears from the noise amplifier. The output of cathode follower V is directly coupled to the lower end of resistor 9 by a conductor 57. It will be understood that so long as cathode follower V remains nonconductive, the potential at thelower end of resistor 9' will be very nearly equal to ground potential. Therefore, by virtue of diode V positive voltages alone are applied to the grid of V However, whenever V conducts, the potential at the lower end of resistor 9' rises considerably above ground potential and therefore results in a reversal of current flow through the resistor to produce negative control voltages at the grid of V A multivibrator 10 of the single-shot type is shown as including tubes V and V, which have their cathodes commonly connected through the magnetizing coil 58 of the magnetic clutch 11. The multivibrator is arranged so that the-application of negative voltages to the grid of V renders V conductive and hence the magnetic clutch 11 rigid or operative. The application, however, of a positive voltage to the grid of V rapidly drives V to cut off, the speed of operation being accentuated by virtue of the common cathode connection of V and V A switch 59 is provided to supply magnetizing current to the clutch 11 in the event it is desired to adjust the receiver during periods when the multivibrator 10 is nonconductive. Aneon lamp 61 connected across the magnetizing coil 58 glows as long as the coil is energized, thereby providing a visual indication of the clutch condition.

In operation, assuming that the receiver 1 is initially off channel and being tuned toward a signal channel, high frequency noise signals will be applied to both the signal amplifier and the noise amplifier. In addition, the noise amplifier receives the direct current and very low frequencies present in the output of the receiver. The noise signals are highly attenuated by the filter 6, but readily passed without undue attenuation by the filter 4. Consequently, the voltage appearing at the anode of V will be relatively high, causing V and hence V and V to conduct. The clutch 44 is therefore rigid and receiver 1 tunable. As the receiver 1 is tuned into the signal channel, characterized by the appearance of a 50 KC signal in the output of the receiver, said output is highly attenuated by filter 4, and readily passed by filter 6. As will be understood, the application of an offchannel frequency modulated signal to a discriminator will result in the production of an output possessing a dc. component. The amplitude of the dc. component decreases as the signal center frequency and the discriminator center frequency approach coincidence. Since the noise amplifier is responsive to do. signals, the noise amplifier maintains an appreciable output until tuning is very nearly exact. As nearly exact tuning is realized, however, it will occur that the voltage appearing at the anode of V is diminished while the voltage appearing at the anode of V is maintained relative- 1y high, or even increased, depending upon the linearity of the discriminator. The combined effect of diminished V anode voltage and increased V anode voltage is to produce a positive control voltage at the grid of V thereby rendering V nonconductive. The clutch 11 therefore returns to a fluid state and is no longer capable of transmitting motion to further adjust the tuning of receiver 1.

Thus, the procedure of locating a signal and accurately tuning the receiver to the frequency of the signal is vastly simplified. It is merely necessary to rapidly adjust the tuning shaft throughout the expected range of signal frequencies. Whenever a signal appears within the range of adjustment, and a precise condition of resonance is attained, the tuning shaft is disengaged at once without the attention of the operator-or without the requirement of monitoring the receiver output to detect the appearance of a signal therein.

Obviously many modifications and variations of the present invent are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In a radio receiver having an input circuit of adjustable reactance and providing an output in the form of a subcarrier characterized by an off-channel direct current component;-a selective signal tuning device, comprising, mechanical means for adjusting the reactance of the input circuit of the receiver, a magnetic clutch having an output element and an input element, said output element being connected to said reactance adjusting means, a tuning control connected to said input element for adjusting said input reactance when said clutch is energized, a first filter receiving said receiver output including said direct current component and adapted to reject the band of frequencies therefrom constituting the subcarrier signal, a second filter receiving said receiver output and adapted to pass the band of frequencies constituting the subcarrier thereof and rejecting the direct current component, means for determining the average output of said first filter, means for comparing the magnitude of the average output of said first filter including said direct current component with the output of said second filter, and means controllable by said comparing means for deenergizing said clutch to arrest adjustment of the reactance of said input circuit whenever the output of said second filter exceeds the average output of said first filter, whereby said receiver is tuned to provide an output constituted by the frequencies passed by said second filter.

2. In a tunable frequency modulation radio receiver having an input circuit of adjustable reactance and providing an output in the from a subcarrier characterized by an off-channel direct current component; a selective signal tuning device, comprising, mechanical means for adjusting the reactance of the input circuit of the receiver, a magnetic clutch having an output element and an input element, said output element being connected to said reactance adjusting means, a tuning control connected to said input element for adjusting said input reactance when a magnetizing current is applied to said clutch, a first filter receiving said receiver out ut and da ted to ass on uts havin fre ue cjes ext nding ron i direct curren to a refativ ly lgh frequency except the band of frequencies constituting the subcarrier which are rejected, a second filter receiving said receiver output and adapted to reject all outputs except those within the band of frequencies constituting the subcarrier, a first amplifier including rectifying means for amplifying and rectifying the output of said first filter, a second amplifier including rectifying means for amplifying and rectifying the output of said second filter, a difference network receiving the outputs of said first and second amplifier and providing a signal having a first polarity whenever the output of said first amplifier exceeds the output of said second amplifier and providing an opposite polarity whenever the output of said second amplifier exceeds the output of said first amplifier, and a multivibrator adapted to apply magnetizing current to said clutch in accordance with the polarity and the output of said difference network, said multivibrator being adapted to magnetize said clutch whenever the output of said first amplifier exceeds the output of said second amplifier, whereby the receiver is tuned to provide an output constituted by the frequencies passed by said second filter. 

1. In a radio receiver having an input circuit of adjustable reactance and providing an output in the form of a subcarrier characterized by an off-channel direct current component; a selective signal tuning device, comprising, mechanical means for adjusting the reactance of the input circuit of the receiver, a magnetic clutch having an output element and an input element, said output element being connected to said reactance adjusting means, a tuning control connected to said input element for adjusting said input reactance when said clutch is energized, a first filter receiving said receiver output including said direct current component and adapted to reject the band of frequencies therefrom constituting the subcarrier signal, a second filter receiving said receiver output and adapted to pass the band of frequencies constituting the subcarrier thereof and rejecting the direct current component, means for determining the average output of said first filter, means for comparing the magnitude of the average output of said first filter including said direct current component with the output of said second filter, and means controllable by said comparing means for deenergizing said clutch to arrest adjustment of the reactance of said input circuit whenever the output of said second filter exceeds the average output of said first filter, whereby said receiver is tuned to provide an output constituted by the frequencies passed by said second filter.
 2. In a tunable frequency modulation radio receiver having an input circuit of adjustable reactance and providing an output in the from a subcarrier characterized by an off-channel direct current component; a selective signal tuning device, comprising, mechanical means for adjusting the reactance of the input circuit of the receiver, a magnetic clutch having an output element and an input element, said output element being connected to said reactance adjusting means, a tuning control connected to said input element for adjusting said input reactance when a magnetizing current is applied to said clutch, a first filter receiving said receiver output and adapted to pass outputs having frequencies extending from direct current to a relatively high frequency except the band of frequencies constituting the subcarrier which are rejected, a second filter receiving said receiver output and adapted to reject all outputs except those within the band of frequencies constituting the subcarrier, a first amplifier including rectifying means for amplifying and rectifying the output of said first filter, a second amplifier including rectifying means for amplifying and rectifying the output of said second filter, a difference network receiving the outputs of said first and second amplifier and providing a signal having a first polarity whenever the output of said first amplifier exceeds the output of said second amplifier and providing an opposite polarity whenever the output of said second amplifier exceeds the output of said first amplifier, and a multivibrator adapted to apply magnetizing current to said clutch in accordance with the polarity and the output of said difference network, said multivibrator being adapted to magnetize said clutch whenever the output of said first amplifier exceeds the output of said second amplifier, whereby the receiver is tuned to provide an output constituted by the frequencies passed by said second filter. 